Gas generating composition

ABSTRACT

There is provided a gas generating composition having good combustion performance. The gas generating composition comprises a fuel, an oxidizing agent and a binder, wherein the binder is at least one selected from polylactone compounds. Poly-ε-caprolactone is preferable as the polylactone compound, and the weight average molecular weight thereof is preferably in the range of 100 to 100,000.

CROSS-REFERENCE TO RELATED APPLICATIONS

This Nonprovisional application claims priority under 35 U.S.C. § 119(e) on U.S. Provisional Application No. 60/578,302 filed on Jun. 10, 2004, the entire contents of which are hereby incorporated by reference.

TECHNICAL FIELD

The present invention relates to a gas generating agent used in a gas generator for an air bag.

BACKGROUND ART

Gas generating agents used in gas generators for air bags generally comprises a fuel, an oxidizing agent, a binder, and various additives.

Hitherto, water-soluble cellulose binders (a starch, carboxymethyl cellulose, guar gum etc.) and polyvinyl alcohol have been widely used as binders due to the moldability being good, but because most fuels and oxidizing agents are also water-soluble, there is a problem that these dissolve in the mixing stage and then recrystallize after drying, and hence a desired grain size cannot be maintained, and thus the intended combustion performance is not obtained.

Moreover, when using a cellulose polymer (a starch, carboxymethyl cellulose, guar gum, cellulose acetate butyrate etc.) as a binder in a gas generating agent, there is a problem that if such a cellulose polymer is combined with ammonium nitrate, which is widely used as a fuel, then the heat resistance of the gas generating agent is greatly reduced.

Furthermore, HTPB (hydroxyl terminated polybutadiene) and GAP (glycidyl azide polymer), which themselves give excellent combustion performance, are also known as organic solvent type binders, but there are problems in terms of being toxic, and a process of removing and recovering a large amount of organic solvent being required meaning that the manufacturing cost is increased.

Prior art to the present invention is WO-A No. 98/9927, US-B No. 5997666, WO-A No. 98/23558, JP-A No. 11-217289, and JP-A No. 9-501388.

DISCLOSURE OF THE INVENTION

The gas generating composition disclosed in WO-A No. 98/9927 uses cellulose acetate butyrate as a binder, the gas generating composition disclosed in US-B No. 5997666 uses polyvinyl alcohol as a binder, and the gas generating composition disclosed in WO-A No. 98/23558 uses HTPB and GAP as binders, and hence there are problems as above in each of these pieces of prior art.

JP-A No. 11-217289 discloses a hybrid inflator using a propellant comprising a secondary explosive and a binder system. This propellant is of a composition for increasing the gas combustion temperature, and realizing a function of breaking a burst disk of the hybrid gas generator at the beginning of combustion. Consequently, the inflator is such that cleaning to an extent permissible for inflator exhaust gas can only be realized once combustion occurs in a gasification stage after the initial combustion of the propellant by a prescribed amount of oxygen in coexisting high-pressure gas, and hence combustion gas cleaning is not obtained merely through combustion of the propellant alone.

JP-A No. 9-501388 discloses polycaprolactam as an example of the binder in a propellant mixture comprising a high-energy binder, but in the use for a propellant mixture, high-level exhaust gas cleaning is not required in particular, and hence the composition is not based on this objective, and thus with the disclosed combination of the high-energy binder, a dinitroamide salt oxidizing agent, a reactive metal and a polyfunctional compound, high-level cleaning of the combustion gas is difficult.

A purpose of the present invention is to provide a gas generating agent according to which the intended combustion performance can be obtained, there is no reaction with ammonium nitrate, and moreover the slag formation ability is good, and hence the amount of a mist spurting out (implying a metal component in the gas generating agent) can be reduced, and thus the combustion gas can be cleaned.

As means for attaining the purpose, the present invention provides a gas generating composition comprising a fuel, an oxidizing agent and at least one binder selected from the group consisting of polylactone compounds, concentrations of ammonia and nitrogen dioxide being substantially 0 ppm in analysis results of a discharged gas after combustion of the composition.

In the present invention, ‘concentrations of ammonia and nitrogen dioxide in discharged gas analysis results after combustion are substantially 0 ppm’ means that the result of measurement using a gas detecting tube is in the range of 0 to X ppm. Here, X indicates the upper limit of the error range for the gas detecting tube.

With the gas generating composition of the present invention, when mixing together the fuel, the oxidizing agent, and the polylactone compound as the binder, a small amount of an organic solvent is added and mixed in, or the polylactone compound is added and mixed in after being thermally melted without a solvent, and then molding can be further carried out; the grain size of the fuel and the oxidizing agent can thus be maintained at a desired grain size, and hence a desired burning rate can be obtained.

Because the gas generating composition of the present invention comprises a polylactone compound as a binder, the amounts of NO₂, NO, NH₃ and CO generated are reduced, and thus the combustion gas is clean; in addition, the slag formation ability is high, and hence the amount of mist spurting out can be reduced.

With the gas generating composition of the present invention, the polylactone compound as the binder does not react with ammonium nitrate, which is widely used as a fuel, and hence even in the case of using together with ammonium nitrate, problems such that the heat resistance of the obtained composition is impaired will not arise.

PREFERRED EMBODIMENT OF THE INVENTION

The gas generating composition of the present invention comprises a fuel, an oxidizing agent, and at least one selected from polylactone compounds as a binder. It is characterized in that a polylactone compound is used as a binder.

A polylactone compound can be dissolved in an organic solvent such as acetone, toluene, xylene, ethyl acetate, butyl acetate, methyl ethyl ketone, methyl isobutyl ketone, isophorone, cellosolve acetate, Solvesso 100 (EXXON MOBIL CORPORATION) or trichlene, and furthermore can be thermally melted without a solvent, and hence the gas generating composition can be manufactured in a non-aqueous system. The problem of the water-soluble fuel and oxidizing agent dissolving in water and recrystallizing so that the grain size changes as in the case of using water in the manufacturing process thus does not occur, and hence a desired grain size can be maintained, and thus the intended combustion performance (burning rate) can be obtained. Note that the burning rate is determined using the method described in the ‘Examples’ section, but can be judged from experience, and hence the burning rate can be set to approximately the desired value (the design value) in advance.

An example of the polylactone compounds is one obtained from a monomer selected from ε-caprolactone (e.g. commercial product of trade name ‘PLACCEL M’ by DAICEL CHEMICAL INDUSTRIES LTD.), a methylated-ε-caprolactone, e.g. 2-methyl-, 4-methyl- or 4,4′-dimethyl one, δ-valerolactone, methylated δ-valerolactone, β-propiolactone and so on. Poly-ε-caprolactone obtained using ε-caprolactone is preferable.

A monomer as above may be used alone, or a plurality of monomers as above may be used copolymerized, or a monomer as above may be polymerized with another monomer such as a polyol or polycarboxylic acid component, or an alloy between a polylactone compound and another polymer compound may be used.

As other monomers, polyols such as ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, propylene glycol, dipropylene glycol, 1,4-butanediol, 1,6-hexanediol, polyols such as glycerol, polyglycerol, trimethylolpropane, polytrimethylolpropane, pentaerythritol and polypentaerythritol, and dicarboxylic acids such as oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, maleic acid, fumaric acid, citric acid, malic acid, tartaric acid and glucaric acid are preferable.

Other polymer compounds that can be mixed in to give a polymer alloy include polyacrylic compounds, polyacetals, urea resins, melamine resins and ketone resins.

Poly-ε-caprolactone can be manufactured using a well-known method, for example the method described in JP-A No. 62-246927, page 3, upper left column.

The polylactone compound preferably has a weight average molecular weight in the range of 100 to 100,000, more preferably 500 to 90,000, yet more preferably 1,000 to 80,000. Note that the weight average molecular weight is that determined through standard PMMA conversion using GPC.

As a poly-ε-caprolactone compound, that of trade name ‘PLACCEL 205’ (weight average molecular weight 530), trade name ‘PLACCEL 208’ (weight average molecular weight 830), trade name ‘PLACCEL 210’ (weight average molecular weight 1,000), trade name ‘PLACCEL 212’ (weight average molecular weight 1,250), trade name ‘PLACCEL 220’ (weight average molecular weight 2,000), trade name ‘PLACCEL 230’ (weight average molecular weight 3,000), trade name ‘PLACCEL 240’ (weight average molecular weight 4,000), trade name ‘PLACCEL HIP’ (weight average molecular weight 10,000), trade name ‘PLACCEL H5’ (weight average molecular weight 50,000) or trade name ‘PLACCEL H7’ (weight average molecular weight at least 70,000) made by DAICEL CHEMICAL INDUSTRIES LTD., or the like can be used.

Other binders may be used together so long as this is within a range such that the object of the present invention can be attained and the effects of the present invention can be obtained; in this case the content of the polylactone compound in the binder is preferably at least 50 mass %, more preferably at least 70 mass %, yet more preferably at least 80 mass %, but it is particularly preferable to use substantially only the polylactone compound as the binder (note, however, that even in this case, it is permitted for small amounts of other binders to be contained either as impurities or to an extent that the effects are not affected at all).

There are no particular limitations on the fuel; examples are ones used in publicly known gas generating agents, and of these nitrogen-containing organic compounds are preferable.

As such a nitrogen-containing organic compound, at least one selected from guanidine nitrate, nitroguanidine, 5-aminotetrazole, dicyandiamide, azodicarbonamide, ammonium nitrate, melamine and glycine can be used. In addition, di- or tri-aminoguanidine nitrate, guanidine carbonate, and nitroaminoguanidine nitrate, bitetrazole derivatives such as diammonium bitetrazole, triazole derivatives such as 4-aminotriazole, triazine derivatives such as trihydrazinotriazine, and oxamide, ammonium oxalate, and hydrazodicarbonamide and so on can also be used.

Of these, guanidine nitrate, nitroguanidine, 5-aminotetrazole, dicyandiamide, and ammonium nitrate are preferable.

There are no particular limitations on the oxidizing agent; examples are ones used in publicly known gas generating agents, and of these inorganic oxidizing agents are preferable.

As an inorganic oxidizing agent, at least one selected from basic copper nitrate, sodium nitrate, potassium nitrate, strontium nitrate, sodium perchlorate, potassium perchlorate and strontium perchlorate can be used. Of these, basic copper nitrate, potassium nitrate, strontium nitrate and potassium perchlorate are preferable.

The gas generating composition of the present invention may as necessary have incorporated therein any of various additives that are incorporated in publicly known gas generating agents. As such additives, at least one selected from metal oxides such as copper oxide, iron oxide, zinc oxide, cobalt oxide, manganese oxide, molybdenum oxide, nickel oxide, bismuth oxide, silica and alumina, metal carbonates or basic metal carbonates such as cobalt carbonate, calcium carbonate, basic zinc carbonate and basic copper carbonate, composite compounds of a metal oxide or hydroxide such as Japanese acid clay, kaolin, talc, bentonite, diatomaceous earth and hydrotalcite, metal acid salts such as sodium silicate, mica molybdate, cobalt molybdate and ammonium molybdate, molybdenum disulfide, calcium stearate, silicon nitride and silicon carbide can be used.

The contents of the various components in the gas generating composition of the present invention can be selected from the following ranges.

For the fuel, preferably 5 to 80 mass %, more preferably 10 to 70 mass %, yet more preferably 20 to 60 mass %, of the composition.

For the oxidizing agent, preferably 10 to 90 mass %, more preferably 20 to 80 mass %, yet more preferably 30 to 60 mass %, of the composition.

For the polylactone compound as a binder, to attain the object of the present invention and obtain the effects of the present invention, preferably 0.1 to 30 mass %, more preferably 0.5 to 20 mass %, yet more preferably 3 to 10 mass %, of the composition.

In addition, in the case of incorporating additives as necessary, 0.01 to 20 parts by mass can be incorporated per 100 parts by mass of the fuel, the oxidizing agent and the binder in total, although this will vary according to the type of the additive.

The gas generating composition of the present invention can be made into a desired molded article having the form of a disk, a cylinder, a single-perforated cylinder, a porous cylinder, pellets or the like.

Because a polylactone compound is used as a binder in the gas generating composition of the present invention, as described in the ‘Examples’ section, the components can be mixed together and molded in a non-aqueous system. As the molding method, a method in which extrusion molding is carried out (for a molded article having the form of a single-perforated cylinder or a porous cylinder), or a method in which compression-molding is carried out using a pelletizer or the like (for a molded article having the form of pellets) can be used; the method described in JP-A No. 2001-342091 can also be used.

The gas generating composition of the present invention can be used, for example, in any of various vehicles in an inflator (gas generator) for an air bag for a driver side, an inflator for an air bag for a front passenger side, an inflator for a side air bag, an inflator for an inflatable curtain, an inflator for a knee bolster, an inflator for an inflatable seat belt, an inflator for a tubular system, or an inflator for a pretensioner.

In addition to use as a gas generating composition for an inflator (gas generator), the gas generating composition of the present invention can also be used as an igniting agent called an enhancer (or a booster) for transferring energy from a detonator or a squib to a gas generating composition.

EXAMPLES

Measurement methods for the examples and comparative examples will now be shown. Note that ‘parts’ in the following means ‘parts by mass’.

(1) Method of Preparing Cylindrical Strand

A powder of the composition of each example and comparative example (a mixed powder for molding, as in Table 1, non-aqueous system for Examples 1 to 3 and Comparative Example 2 was filled into the mortar side of a prescribed die, compression at a pressure of 14.7 MPa was held for five seconds using a hydraulic pump from the end face on the pestle side, and then the molded article was taken out, whereby molding into a cylindrical strand having an outside diameter of 9.55 mm and a length of 12.70 mm was carried out. An epoxy resin-based chemical reaction-type adhesive, ‘BONDQUICK 30’ made by KONISHI CO., LTD., was applied onto the side surface of the cylindrically molded article and then thermosetting was carried out for 16 hours at 110° C. to obtain a sample which will ignite and burn not in the side surface, but in the end surface only so that the combustion may transfer in a single plane.

(2) Method of Measuring Burning Rate

Each sample cylindrical strand was installed in an SUS sealed chamber having an internal volume of 1 L, and while completely purging the inside of the chamber with nitrogen, pressurization up to and stabilization at 7 MPa was carried out. After that, a prescribed current was passed into a nichrome wire in contact with an end face of the strand, thus carrying out ignition and hence combustion through the fusing energy of the nichrome wire. The behavior of the pressure over time in the chamber was determined using a recorder chart, the time elapsed from the start of combustion until the pressure peaked was determined from the scale on the chart, and the value calculated by dividing the length of the strand before combustion by the elapsed time was taken as the burning rate.

(3) Method of Measuring Gas Concentrations

Each sample cylindrical strand (mass 2.00 g) was installed in an SUS sealed chamber having an internal volume of 1 L, and while completely purging the inside of the chamber with nitrogen, pressurization up to and stabilization at 7 MPa was carried out. After that, a prescribed current was passed into a nichrome wire in contact with an end face of the strand, thus carrying out ignition and hence combustion through the fusing energy of the nichrome wire. 60 seconds was waited so that the gas in the chamber would become uniform, and then an open stopper portion of a prescribed stopper-possessing Tedlar bag was connected to a gas discharge portion of the chamber, a sample was taken by transferring the combustion gas in the chamber into the Tedlar bag, and the concentrations of NO₂, NO, NH₃ and CO were measured by Gastec gas detecting tubes (no. 10 for detecting NO₂ and NO, no. 3L for detecting NH₃, and no. 1L for detecting CO) using a GV-100S detector made by GASTEC CO.,.

(4) Mass of Recovered Residue

After the above ‘(3) Method of measuring gas concentrations’ test had been completed, the state inside the chamber was visually observed, and moreover the residue inside the chamber was recovered, and the mass thereof was measured after drying for 16 hours at 110° C.

(5) Mass Reduction Rate

Each sample cylindrical strand (mass 2.00 g) was left in a thermostatic chamber for 400 hours at 110° C., and then the mass reduction rate was determined from the following formula. Mass reduction rate (%)=(Mass before test−Mass after test)×100/Mass before test (6) Weight Average Molecular Weight by GPC

The weight average molecular weight was determined through standard PMMA conversion. Shodex GPC HFIP-800P, HFIP-805P, HFIP-804P and HFIP-803P made by SHOWA DENKO K.K. were used as a column, RID-6A made by SHIMADZU CORPORATION was used as a detector, and HFIP was used as an eluent, and measurement was carried out at a column temperature of 50° C. and a flow rate of 1.0 ml/min.

Example 1

42.44 parts of guanidine nitrate, 30.76 parts of ammonium nitrate, and 21.80 parts of potassium perchlorate were passed twice through an SUS sieve having a 300 μm mesh to make the grains uniform, and were mixed together to obtain a mixed powder.

5 parts of ‘PLACCEL 240’ (trade name, weight average molecular weight 4000) made by DAICEL CHEMICAL INDUSTRIES LTD. as a polylactone compound was mixed with 40 parts of acetone, and was dissolved while heating to 60° C., and then the resulting solution was added to 95 parts of the above mixed powder, and thorough mixing was carried out. After that, drying was carried out for 1 hour at 110° C. to obtain a composition of the present invention, and then molding into a cylindrical strand was further carried out using the method described above. The measurement results are shown in Table 1.

Example 2

Using 51.35 parts of guanidine nitrate, 43.65 parts of potassium perchlorate, and 5 parts of ‘PLACCEL HIP’ (trade name, weight average molecular weight 10,000) made by DAICEL CHEMICAL INDUSTRIES LTD. as a polylactone compound, a composition of the present invention was obtained as in Example 1, and then molding into a cylindrical strand was further carried out using the method described above. The measurement results are shown in Table 1.

Example 3

42.44 parts of guanidine nitrate and 21.80 parts of potassium perchlorate were passed twice through an SUS sieve having a 300 μm mesh to make the grains uniform, and were mixed together to obtain a mixed powder.

5 parts of ‘PLACCEL H5’ (trade name, weight average molecular weight 50,000) made by DAICEL CHEMICAL INDUSTRIES LTD. as a polylactone compound was melted while heating up to 80° C., and was then added to 95 parts of the above mixed powder, and thorough mixing was carried out, after which drying was carried out for 1 hour at 110° C. to obtain a composition of the present invention, and then molding into a cylindrical strand was further carried out using the method described above. The measurement results are shown in Table 1.

Comparative Example 1

42.44 parts of guanidine nitrate, 28.36 parts of ammonium nitrate, and 18.10 parts of potassium perchlorate were passed twice through an SUS sieve having a 300 μm mesh to make the grains uniform, and were mixed together to obtain a composition, and then molding into a cylindrical strand was further carried out using the method described above. The measurement results are shown in Table 1.

Comparative Example 2

42.44 parts of guanidine nitrate, 30.76 parts of ammonium nitrate, 21.80 parts of potassium perchlorate and 5.00 parts of carboxymethyl cellulose were passed twice through an SUS sieve having a 300 μm mesh to make the grains uniform, and were mixed together to obtain a composition, and then molding into a cylindrical strand was further carried out using the method described above. The measurement results are shown in Table 1. TABLE 1 Comparative Comparative Example 1 Example 2 Example 3 Example 1 Example 2 Guanidine nitrate 42.44 51.35 42.44 53.54 42.44 (parts) Ammonium nitrate 30.76 — — 28.36 30.76 (parts) Potassium perchlorate 21.8 43.65 21.80 18.10 21.80 (parts) Binder (parts) PLACCEL PLACCEL PLACCEL H5 (5) — Carboxymethyl 240 (5) HIP (5) cellulose (5) Solvent when adding Acetone Acetone None — Water binder (thermally melted) Burning rate (mm/sec) 7.97 15.75 13.63 7.81 8.66 Gas NO₂ 0 0 0 0 0 concentrations NO 60 27 9 41 29 (ppm) NH₃ 0 0 0 19 30 CO 570 380 300 350 450 Mass of residue (g) 0.21*¹ 0.39*² — — — Mass reduction rate (%) 0.24 0.31 0.16 Cracks, not 6.24*³ original shape *¹Cleaner than with the comparative examples, and only 5 white particles of size at least 1 mm observed as residue with good slag form. *²Cleaner than with the comparative examples, and only 7 white particles of size at least 1 mm observed as residue with slag form. *³Discolored from initial white to brown, and underwent deformation.

The burning rate for Examples 1 to 3 was similar to the original design value. This means that, because molding was carried out after adding and mixing in acetone or adding and mixing in a thermally melted polylactone compound without a solvent in the mixing stage, the original grain size (the grain size that passed through the sieve) of the fuel and the oxidizing agent was maintained. Moreover, even in the case that acetone is used, compared with the case that an organic solvent is used as a binder, the operation to recover and thus remove the solvent is easy.

As is clear from the mass of residue for Examples 1 and 2, the slag formation ability is high, and hence the amount of mist spurting out can be reduced.

As is clear from a comparison of the mass reduction rate between Example 1 and Comparative Examples 1 and 2, for Example 1 the heat resistance was excellent despite ammonium nitrate being contained. 

1. A gas generating composition comprising a fuel, an oxidizing agent and at least one binder selected from the group consisting of polylactone compounds, concentrations of ammonia and nitrogen dioxide being substantially 0 ppm in analysis results of a discharged gas after combustion of the composition.
 2. The gas generating composition as claimed in claim 1, wherein the weight average molecular weight of the polylactone compound is 100 to 100,000.
 3. The gas generating composition as claimed in claim 1, wherein the fuel is a nitrogen-containing organic compound, the oxidizing agent is an inorganic oxidizing agent, and the gas generating composition further comprises additives as necessary.
 4. The gas generating composition as claimed in claim 2, wherein the fuel is a nitrogen-containing organic compound, the oxidizing agent is an inorganic oxidizing agent, and the gas generating composition further comprises additives as necessary.
 5. The gas generating composition as claimed in claim 1, wherein the nitrogen-containing organic compound is at least one selected from the group consisting of guanidine nitrate, nitroguanidine, 5-aminotetrazole, dicyandiamide, azodicarbonamide, ammonium nitrate, melamine and glycine.
 6. The gas generating composition as claimed in claim 2, wherein the nitrogen-containing organic compound is at least one selected from the group consisting of guanidine nitrate, nitroguanidine, 5-aminotetrazole, dicyandiamide, azodicarbonamide, ammonium nitrate, melamine and glycine.
 7. The gas generating composition as claimed in claim 1, wherein the inorganic oxidizing agent is at least one selected from the group consisting of basic copper nitrate, sodium nitrate, potassium nitrate, strontium nitrate, sodium perchlorate, potassium perchlorate and strontium perchlorate.
 8. The gas generating composition as claimed in claim 2, wherein the inorganic oxidizing agent is at least one selected from the group consisting of basic copper nitrate, sodium nitrate, potassium nitrate, strontium nitrate, sodium perchlorate, potassium perchlorate and strontium perchlorate. 